Sounds like your are understandably in a stress-inducing situation. I find that often around this age the prospect of future careers becomes more daunting and realistic as many young adults are no longer just studying but also finding post-graduate jobs. I understand how this can be an anxious time for you given the instability of COVID-19 paired with the competitiveness in your field of study and interest.
I'm glad you have taken the initiative to widen your experience and have gotten involved with some volunteer work and even looked into further skills and studies. This is a great step forward, as you are not only dwelling in your emotions but also taking effective action towards a practical plan. This shows you have initiative and adaptability, I think these are key assets in the working environment and definitely would disagree that you don't have any marketable skills!
However, I understand that when in a competitive field it is difficult to not compare yourselves to others and not to be over critical of your shortcomings. I am also 20 and like you I have also recently found myself in an anxious situation where I felt like my field was too competitive. However, upon further research I found there are multiple options and pathways to my desired course or desired career. I think having a "hope for the best, but prepare for the worst" mentality is good as it assures that you are well-equipped and prepared if plan A falls through, however I also think having a "where there is a will, there is a way" mentality is equally important as it assures you that no matter what you do, if you have the will and passion, there will always be a way to a fulfilling career or successful path.
I find that many people can have a way and are doing essentially what they had planned, however I also find that a proportion of people also lack the will and passion in what they do. Therefore, I think rather than finding a way, it is the will that is most essential to guaranteeing you a fulfilling future. I think what you have done so far is great, definitely improving your qualifications, knowledge and resume building will help with future job prospects, however maintaining that beautiful passion of yours is just as important!
It sounds as though you have supportive family and friends, don't let that make you feel guilty but allow yourself to feel grateful and use that strength to accomplish what you wish to do. I hope you are able to find your way and do what you love